Today's public switched telephone networks use signalling system no. 7 (SS7) telephony signalling protocols mainly to set up and tear down telephone calls, as well as for extended services. The SS7 network comprises signalling end points (SEP), such as services switching points (SSP), e.g. a local exchange. The SS7 network may further comprise signalling transfer points (STP), which are essentially routers which relay SS7 messages between signalling end points. The SS7 network generally uses message transfer part (MTP) 1-3 protocols for the transport of signalling messages. In an STP, routing is for example performed by the MTP-3 layer. A user of the MTP-3 services is for example the signalling connection control part (SCCP) network layer, which provides extended routing capabilities, flow control and segmentation. SCCP also supports a connection oriented mode for the transport of signalling messages, in which an end-to-end connection is established before exchanging data between signalling end points.
For transporting SS7 messages over an Internet protocol (IP) network, the SS7 network and the IP network are connected by a signalling gateway (SG). The signalling gateway adapts the SS7 messages for a transport in the IP network. The adapted messages are then transported in the IP network using user adaptation protocols, for which the signalling gateway implements for example an MTP-3 user adaptation (M3UA) layer or an SCCP user adaptation (SUA) layer. For transport of the user adaptation messages in the IP network, the stream control transmission protocol (SCTP) is generally used. Accordingly, the signalling gateway further implements an SCTP layer and an IP layer. The signalling gateway uses an interworking function to provide an interworking between the MTP3 layer and the M3UA layer or the SCCP layer and the SUA layer. Details on the M3UA and the SUA protocols are given in RFC 4666 and RFC 3868, respectively.
Like SCCP, SUA supports a connection oriented mode for the transfer of signalling messages. In the connection oriented mode, the signalling gateway establishes a connection section towards a remote peer network node. Similarly, the SCCP layer on the signalling gateway establishes a connection section towards the remote SS7 signalling end point. The connection sections are coupled in the signalling gateway, whereby the connection between the signalling end point in the IP and the signalling end point in the SS7 network is established. Once the connection is established, connection oriented data messages can now be easily transferred between the signalling end points via the signalling gateway.
In case that the signalling gateway fails, all the connections coupled at the signalling gateway will be lost. In consequence, corresponding calls for which signalling messages were exchanged via the established connections may also be lost. This may lead to losses in revenue for the operator of the telephony network. Furthermore, the requirements for signalling gateway reliability need to be increased in order to prevent such a loss, which in turn requires more complex signalling gateway architectures and results in higher development costs. Accordingly, there is a need to overcome these drawbacks. In particular, there is need of providing a method which improves the transport of connection oriented messages over a signalling gateway. It is further desirable to provide a signalling gateway and an application server capable of implementing such an improved method of transporting connection oriented signalling messages. It is also desirable to increase the in service performance of a signalling gateway.